Coastal Restoration Trust of New Zealand

Coastal Dune Ecosystem Reference Database

Coastal Dand Dunes - Form and Function Bulletin

Author
Hesp, P.A.
Year
2000
Journal / Source
Coastal Dune Vegetation Network Technical Bulletin
Publisher / Organisation
New Zealand Forest Research Institute Limited
Number
4
Pages
28
Keywords
coastal landforms, pumice layers, marker layers, radiocarbon dating, geomorphology, archaeology, Holocene, deposition
Summary
Loisels Pumice is a sea-rafted pumice of uncertain origin, found on the east coast of the North Island of New Zealand. Since a radiocarbon age range was compiled from different and indirectly dated pumice layers by McFadgen (1982), Loisels Pumice has been used as a stratigraphic marker layer of known age in late Holocene coastal deposits. We contend that the date of primary deposition has been incorrectly determined and applied. We examined field sections from the far north of the North Island to identify and date the primary deposition of Loisels Pumice and to describe the physical characteristics and value of such a deposit. We also critically examined sites identified in the literature. Only one deposit was potentially primary, and the age of pumice deposition could be closely bracketed. From this section, we propose an age range of 915-1030 cal AD for the first stranding of Loisels Pumice in northern New Zealand. Analysis of sections shows that stratigraphic and geomorphic interpretation may be used to identify sites with the potential to be primary, but primary and secondary deposits cannot be identified by descriptive statistics. We conclude that the age of first stranding of Loisels Pumice cannot be reliably derived by compiling an age range bracket using maximum and minimum dates from different sections. Loisels Pumice should not be used as a coastal marker layer to establish synchrony between sites, and recent interpretations based on this method should be re-appraised.
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